Advancements in the fields of analytical chemistry and biomedical technology have stressed the need for more efficient means of analyses with faster analysis times, smaller sample and reagent consumption, higher efficiency, greater apparatus portability and easier use. Capillary Electrophoresis (CE) is a commonly used separation technique, which makes use of differences in the charge ratio of components in a mixture. CE generally includes a capillary placed between two electrodes linked by a voltage source. The capillary is filled with an electrolyte such as an aqueous buffer solution. A sample of a material to be tested is also introduced into the capillary.
Testing is initiated by applying an electric field between the electrodes. All ions, positive or negative, are pulled through the capillary in the same direction by electroosmotic flow. The field also causes the components of the material being tested, referred to as analytes, to separate as they migrate toward the cathode due to their electrophoretic mobility. The rate of migration differs depending on the analytes particular electrokinetic mobility. These analytes are detected near the outlet end of the capillary. Analytes can generally be identified through knowledge of the electric field applied, the geometry of the capillary, the distance of migration, and the time required to migrate that distance. For example, in a mixture of dopamine and catechol, dopamine having the higher electrokinetic mobility would reach the cathode faster than catechol, which has a lower electrokinetic mobility. Separation by capillary electrophoresis can be detected by several detection methodologies, including by way of example but not limited to, ultraviolet (UV) or UV-Vis absorbance, fluorescence detection, electrochemical detection or mass spectrometery.
One limitation of some capillary electrophoresis systems and methods is that samples which contain analytes with equal or near-equal mobilities cannot be readily separated. For two analytes having substantially equal mobilities, for example, migration in a CE capillary or microchannel will be at essentially the same velocity and therefore may be difficult to conclusively detect. Detection errors may result, such as inaccurately detecting the concentration of analytes, or analyte misidentification.
In addition, like many analysis techniques, CE procedures often call for highly reliable test results. Such reliability may require redundant testing of samples. Many current systems and techniques require multiple test runs or multiple samples to accomplish redundant results. Multiple test runs or samples increase total testing time and introduce a risk that the sample may be contaminated or otherwise be inconsistent between test runs. In addition, larger volumes of sample are required, which may or may not always be available and will increase the cost of the process.
Still an additional problem with some CE systems and methods of the prior art related to achieving test analyte samples (or “plugs”) in a detection channel having a good geometry. Some systems of the prior art use a configuration that provides poorly defined sample plugs. Other systems require multiple power supplies to generate multiple electric fields to produce sample plugs, which results in complex and extensive circuitry and system size as well as other disadvantages. These and other problems make some CE systems of the prior art ill-suited for field and related applications where portability is desired.
These and other problems remain unresolved in the art.